The natural lens of a human eye is a transparent crystalline body, which is contained within a capsular bag located behind the iris and in front of the vitreous cavity in a region known as the posterior chamber. The capsular bag is attached on all sides by fibers, called zonules, to a muscular ciliary body. At its rear, the vitreous cavity, which is filled with a gel, further includes the retina, on which light rays passing through the lens are focused. Contraction and relaxation of the ciliary bodies changes the shape of the bag and of the natural lens therein, thereby enabling the eye to focus light rays on the retina originating from objects at various distances.
Cataracts occur when the natural lens of the eye or of its surrounding transparent membrane becomes clouded and obstructs the passage of light resulting in various degrees of blindness. To correct this condition in a patient, a surgical procedure is known to be performed in which the clouded natural lens, or cataract, is extracted and replaced by an artificial intraocular lens. During cataract surgery, the anterior portion of the capsular bag is removed along with the cataract, and the posterior portion of the capsular bag, called the posterior capsule, is sometimes left intact to serve as a support site for implanting the intraocular lens. Such lenses, however, have the drawback that they have a fixed refractive power and are therefore unable to change their focus.
Various types of intraocular lenses having the capability of altering their refractive power have been suggested in an effort to duplicate the performance of the natural lens within the eye. Such accommodating intraocular lenses, as they are known in the art, have a variety of designs directed to enable the patient to focus on, and thereby clearly see, objects located at a plurality of distances. Examples may be found in such publications as U.S. Pat. No. 4,254,509, U.S. Pat. No. 4,932,966, U.S. Pat. No. 6,299,641, and U.S. Pat. No. 6,406,494.
U.S. Pat. No. 5,489,302 discloses an accommodating intraocular lens for implantation in the posterior chamber of the eye. This lens comprises a short tubular rigid frame and transparent and resilient membrane attached thereto at its bases. The frame and the membranes confine a sealed space filled with a gas. The frame includes flexible regions attached via haptics to the posterior capsule. Upon stretching of the capsule by the eye's ciliary muscles, the flexible regions are pulled apart, thereby increasing the volume and decreasing the pressure within the sealed space. This changes the curvature of the membranes and accordingly, the refractive power of the lens.
U.S. Pat. No. 6,117,171 discloses an accommodating intraocular lens which is contained inside an encapsulating rigid shell so as to make it substantially insensitive to changes in the intraocular environment. The lens is adapted to be implanted within the posterior capsule and comprises a flexible transparent membrane, which divides the interior of the intraocular lens into separate front and rear spaces, each filled with a fluid having a different refractive index. The periphery of the rear space is attached to haptics, which are in turn attached to the posterior capsule. Upon stretching of the capsule by the eye's ciliary muscles, the haptics and hence this periphery is twisted apart to increase the volume of rear space and changes the pressure difference between the spaces. As a result, the curvature of the membrane and accordingly, the refractive power of the lens changes.